Duo-signaling system



Oct. 22, 1935, w s BARDEN ET AL 2,017,886

DUO-SIGNALING SYSTEM Filed March 21, 1952 3 Sheets-Sheet 2 INVENTORS WILLIAM S. BARDEN BY WALTER v2. ROBERTS AT'TOFRNEY Oct. 22, 1935, w 5 BARDEN ET AL 7 2,017,886

DUO-SIGNALING SYSTEM Filed March 21, 1952 3 Sheets-Sheet 5 ffifGUfA/CY CHANGER t INVENTORS WILLIAM s. BARDEN WALTER vqn BROBERTS ATTORNEY face/Vex" Patented Oct. 22, 1935 UNITE ST PATENT OFFHQE DUO-SIGNALING SYSTEM William S. Barden, Stapleton, N. Y., and Walter van B. Roberts, Princeton, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application March 21,

3 Claims.

'5 and relates more particularly to carrier plus double side band systems wherein all of an allowed frequency band may be utilized by the side bands of both signals.

Heretofore, radio signaling systems have not permitted each of the intelligences superimposed on a carrier to occupy identical portions of the spectrum. For example, systems proposed in the past to accomplish radio signaling duplexing have not been able to permit Yankee Doodle, as an illustration, to be one program covering all audio frequencies, and Turkey in the Straw as the other program covering all audio frequencies, to be superimposed and transmitted as modulation of a single carrier.

One of the main objects of this invention is to simultaneously transmit two intelligence signals on the same wave length, each independent formation of intelligence being unrestricted as regards audio frequency components.

Another important object of this invention is to provide novel and efiicient means for the formation of what will be referred to as a complex signa at the transmitter, and to provide novel and efficient devices for analyzing the complex signal at the receiver.

Still another object of this invention is to provide a duo-signaling system capable of transmitting different intelligences, such as television and audio frequency accompaniment, on the same frequency band, and to particularly provide a system wherein two stations transmit such a complex signal from the same antenna and on the same carrier.

The novel features which we believe to be characteristic of our invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawings in which we have indicated diagrammatically several arrangements whereby our invention may be carried into effect.

In the drawings,

Fig. 1 is a schematic representation of a transmitter incorporating the invention,

Fig. 2 illustrates diagrammatically the schematic transmitter of Fig. 1,

Fig. 3 is a schematic showing of a receiver incorporating the invention,

Fig. 4 is a diagrammatic showing of a preferred 1932, Serial No. 600,152

embodiment of the schematic receiver shown in V v Fig. 3,

Fig. 5 illustrates diagrammatically a phase control device adapted for use in the receiver of Fig. l, 5

Fig. 6 graphically illustrates the characteristic curve of the tubes used in the phase control of the receiver of Fig. 4.

Referring now to the accompanying drawings for a complete disclosure of the invention, it may 10 be shown that an ideal Heising-modulated wave train may have its percentage of modulation reduced to zero by applying a ninety degree phase shift to the carrier. When two ideal Heisingmodulated wave trains co-exist with their car- 1 riers in time quadrature and identical in frequency, the result is a complex signal which may be analyzed by properly alternating the carrier phase.

A preferred method of accomplishing the car- 20 rier phase shift at the receiver derives a pure carrier from the signal itself, and employs it in such a manner that the effective carrier has the desired phase without dependence upon magnitudes.

Referring now to Fig. 1, there is shown a representative transmitter embodying a master oscillator at I, two independent sources of modulating signals at 2 and 3, a phase control at 4 adapted to present carriers in time quadrature to Heising tube modulators at 5 and 6, and a coupling arrangement at I adapted to present the complex signal to a power amplifier at 8. The complex signal is then fed to the usual grounded antenna means for transmission by radiation. Of 35 course any other type of transmission medium may be employed, as a conductor.

While various circuit arrangements are possible without departing from the scope or spirit of this invention, a preferable transmitter circuit arrangement is shown in Fig. 2, wherein a master oscillator I supplies energy at a carrier frequency to the secondary 9. The latter is tuned by a condenser Ifi when the arrangement, comprising equal inductances II and I2, condensers I3 and 5 I4, and resistances I5 and I6, is so designed that the carrier voltages across inductances H and I2 are equal and in time quadrature. Modulator tubes IT and I8, with their associated circuits, output the above mentioned two I-Ieising-modu- 5o lated signals with carriers in time quadrature at I9 and 20. Each of the inductances 2| and 22 performs the function of a variable impedance as embodied in a typical and well known Heising modulating system. A condenser bridge 23 may 5 be used to combine the two modulated wave trains without coupling their sources, the complex signal being available across any bridge arm, such as 24, for presentation to a power amplifier 8, the latter being coupled to the antenna circuit.

At the receiver various circuit arrangements are possible without departure from the scope or spirit of this invention. Fig. 3 represents the essentials of a typical receiver; 25 designates a device which may select and amplify the complex signal. The latter is then presented to de tectors at 21 and 28. A following device at 2B outputs pure carriers at proper phases to said detectors, or analyzers, at 21 and 28. heterodyne type of receiver is employed at 25, the circuits at 26, 21 and 2% may be permanently adjusted to function at the intermediate frequency band.

A preferable receiver circuit arrangement eliminates second order effects which occur to those skilled in the art. as well as obtains ideal analyzing without dependence upon constancyof incoming carrier magnitude. Such an arrangement is shown in Fig. 4 wherein coil 29 may be the last tuned secondary of an amplifier operating at the intermediate frequency band. The coii 29 is shown coupled to the output of the conventional intermediate frequency amplifier of a superheterodyne receiver.

Secondary 29 is tuned by the effective capac itance oi the several devices in shunt to it. The

'eifective capacitance of bridges 39 and 3!, plus the capitance due'to tube .3, is in shunt to a portion of secondary 29, condenser 32 being in shunt to the remaining portion. When both these portions are equal it is. desirable that each shall have the same amount of shunted capacitance. Condenser 33 is in shunt to all of secondary 29, for tuning.

Tubes 34 and 35 with their associated circuits function as a push-pull detector, and the output of said push-pull circuit supplies the potential of one signal across A-B. Tubes 36 and 31 with their associated circuits function as a push-pull detector, and the output of said push-pull circuit supplies the potential of the other signal across C-D. The output arrangement shown is adapted to the requirements of television when 38, 39, 40 and M are resistances.

It has been sated that the complex signal may be analyzed by applying a proper phase shift to the carrier, effectively. When the circuit arrangement renders the incoming carrier inoperative as an analyzer, a local carrier may be applied of the proper phase. The result is as though the incoming carrier were removed, and replaced by another carrier of the desired phase. This is accomplished by impressing a carrier across each bridge 30 and 3|, as shown, where 4 l and 42 impress carriers in time quadrature.

4| impresses a carrier which is in phase with the carrier of one signal, 1. e. the output of one modulator such as at [9. 42 impresses a carrier which is in phase with the carrier of theother signal, i. e. the output of the other modulator at 20. Since II and i2 apply carriers in time quadrature to the modulators, ii and 42 must also apply carriers in time quadrature. These relations, and the performance of the push-pull detectors which output no distortion or interference due to cross heterodyne effects when both sides of the detectors are effectively identical, will be apparent to those skilled in the art. 3

The carriers at 4| and 2 are derived from the incoming signal by a method which is an im- When a portant feature of this invention. It may be shown that plate current saturation in a triode of usual design may be obtained at negative grid potential when a proper relation of anode potential to cathode temperature is established. In 5 general, this relation is conveniently established when the anode potential is abnormal and the cathode temperature subnormal with respect to rated values. A tube can readily be designed for plate current saturation at negative grid is potential as a normal condition. Fig. 6 shows the static characteristic of such a tube.

Tubes 43, 44 and 45 have that characteristic, and are grid biased with B volts to obtain about half of saturation plate current, as shown. Each of these three tubes function as a demodulator when the modulated signal applied to the grid circuit is demodulated in the plate circuit which then contains a carrier with its odd harmonics, and relatively reduced side band components with their odd harmonics. When two stages of demodulation are employed with moderately selective circuits, the output is an essentially pure carrier for use at the analyzers. When Q is several times R, as shown, the output carrier magnitude is essentially independent of moderate variations in applied carrier magnitude.

Peak modulation of the complex signal should not exceed perhaps for convenience in demodulator design, aithough it will be apparent to those skilled in the art that peak modulation could be accommodated with no great hardship. To avoid an unusual degree of amplification ahead of the first demodulator tube a3, a tube may be chosen which requires only a few grid volts, say 3 four or five, to sweep from plate current cut-off to plate current saturation. With such a tube, the grid bias B may be 10, or preferably 20 volts.

The degree of demodulation is determined by the dynamic characteristic of the tube and its 40, associated devices, and to obtain a favorable one the'tuned impedance appearing in'the plate circuit of a demodulator tube should not exceed perhaps one fourth of the tube impedance Rp- When the demodulator tube is of the high mu 45 type, such as UX-Edfl, a compromise between amplification and demodulation may well be made in favor of the latter.

Of course, it is desirable that no signal potential shall reach secondary 45 which has not been sub- 50 jected to demodulation, or side band component suppression as it may be termed. For this reason, as Well as to prevent oscillation, condenser 41 is employed as in a typical Rice neutralization circuit. For these purposes, a Rice neutralization 55 circuit, or the equivalent which may take a variety of forms, is associated with all demodulator tubes 35, 44, and 45 as shown.

The carriers at 4| and 42 are delivered. by demodulator tubes 45 and it, respectively, and 60 are caused to be in time quadrature by applying carriers in time quadrature to the grid circuits of these tubes. Inductances 48 and 49 perform this function, and to this end secondary 46 is tuned by condenser 50. The arrangement of the equal 65 inductances 4B and 49, condensers 5| and 52 and resistances 53 and 54 are so designed that the impedance across UV is a pure resistance, and the carrier potentials across 48 and 49 are equal.

It will be apparent to those skilled in the art 70 that when the modulators shown in Fig. 2 deliver carriers of equal magnitudes at I9 and 20, the resultant carrier at 24 is such that the carrier of one signal lags it by 45, and the carrier of the other signal leads it by 45. It is this resultant 76 carrier from which the inductances 48 and 49 must apply components, one lagging it by 45, the other leading it by 45. For this principal reason, it is essential that condenser 55 shall tune secondary 45 to resonance at the carrier'frequency.

While there is no great hardship connected with a requirement that the modulators shall deliver carriers of equal magnitudes at I9 and 2%, thus simplifying the phase control at the receiver, a more flexible phase control at the receiver permits the modulators to deliver unequal carrier magnitudes at l9 and 20. In Fig. 5, there is shown such a flexible phase control device wherein inductances 48 and 49 are in space quadrature, two adjustable rotors 55 and 55 being space phased to apply carriers at proper time phases to tubes 44 and 45. When the transmitter is modified to radiate a complex signal comprising an ideal Heising-modulated wave train with its carrier in phase with the carrier of an ideal Heisingmodulated wave train which has had its percentage of modulation reduced to zero by virtue of a 90 carrier phase shift, thus permitting existing receivers to reproduce one signal without interference from the other (except due to second order effects which would be tolerable when the peak percentage of modulation was moderate before shifting the carrier phase), the more flexible arrangement shown in Fig. becomes desirable.

While We have indicated and described several systems for carrying our invention into efiect, it will be apparent to one skilled in the art that our invention is by no means limited to the particular organizations shown and described, but that many modifications may be made Without departing from the scope of our invention as set forth in the appended claims.

What we claim is:

1. Means for receiving a plurality of difierent signals on a complex wave including, signal receiving and amplifying means, a plurality of detectors, there being a detector for each separate signal transmitted, each detector comprising, a pair of thermionic tubes having their output electrodes connected in push-pull relation, a Wheatstone bridge circuit coupled by way of one of its diagonals to the control grids of said tubes, means for impressing received signal on the other diagonal of said bridge circuit, a circuit for separating carrier energy only from said received signal, thermionic means for separating said separated carrier into separate portions and for producing a phase shift between said portions, and a circuit for applying energy from each of said phase shifted portions differentially to the control grids of the tubes in each of said detectors.

2. Means for receiving a plurality of different signals on a complex wave including, signal receiving and amplifying means, a plurality of detectors, there being a detector for each separate signal transmitted, each detector comprising, a pair of thermionic tubes having their output electrodes connected in push-pull relation, a bridge circuit coupled by way of one of its diagonals between the control grids of the tubes of each pair, means for impressing received signals in phase on the other diagonal of each of said bridge circuits, a circuit coupled with said receiving and amplifying means for separating carrier energy only from said received signal, thermionic means coupled to said last named circuit for dividing said separated carrier energy into separate portions and for producing a 90 phase shift between said portions, and circuits for applying energy from one of said phase shifted portions differentially to the control grids of the tubes in each of said detectors.

3. Means for receiving a. plurality of different signals on a complex wave including, signa1 receiving and amplifying means, a plurality of detectors, there being a detector for each separate signal transmitted, each detector comprising, a pair of thermionic tubes having their output electrodes connected in push-pull relation, a bridge circuit coupled by way of one of its diagonals to the control grids of the tubes of each pair, there being a bridge circuit for each pair, a circuit for impressing signals from said receiving and amplifying means in phase on the other diagonal of each of said bridge circuits, a circuit coupled with a energy in the several portions, and separate inductive means coupled on the one hand with said last named thermionic means and on the other hand with the first mentioned diagonal in each of said bridge circuits for impressing thereon carrier energy.

WILLIAM S. BARDEN. WALTER VAN B. ROBERTS. 

